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1<?xml version="1.0" encoding="UTF-8" standalone="no"?>2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>ALTER TABLE</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="sql-altersystem.html" title="ALTER SYSTEM" /><link rel="next" href="sql-altertablespace.html" title="ALTER TABLESPACE" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">ALTER TABLE</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="sql-altersystem.html" title="ALTER SYSTEM">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="sql-commands.html" title="SQL Commands">Up</a></td><th width="60%" align="center">SQL Commands</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="sql-altertablespace.html" title="ALTER TABLESPACE">Next</a></td></tr></table><hr /></div><div class="refentry" id="SQL-ALTERTABLE"><div class="titlepage"></div><a id="id-1.9.3.35.1" class="indexterm"></a><div class="refnamediv"><h2><span class="refentrytitle">ALTER TABLE</span></h2><p>ALTER TABLE — change the definition of a table</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><pre class="synopsis">3ALTER TABLE [ IF EXISTS ] [ ONLY ] <em class="replaceable"><code>name</code></em> [ * ]4    <em class="replaceable"><code>action</code></em> [, ... ]5ALTER TABLE [ IF EXISTS ] [ ONLY ] <em class="replaceable"><code>name</code></em> [ * ]6    RENAME [ COLUMN ] <em class="replaceable"><code>column_name</code></em> TO <em class="replaceable"><code>new_column_name</code></em>7ALTER TABLE [ IF EXISTS ] [ ONLY ] <em class="replaceable"><code>name</code></em> [ * ]8    RENAME CONSTRAINT <em class="replaceable"><code>constraint_name</code></em> TO <em class="replaceable"><code>new_constraint_name</code></em>9ALTER TABLE [ IF EXISTS ] <em class="replaceable"><code>name</code></em>10    RENAME TO <em class="replaceable"><code>new_name</code></em>11ALTER TABLE [ IF EXISTS ] <em class="replaceable"><code>name</code></em>12    SET SCHEMA <em class="replaceable"><code>new_schema</code></em>13ALTER TABLE ALL IN TABLESPACE <em class="replaceable"><code>name</code></em> [ OWNED BY <em class="replaceable"><code>role_name</code></em> [, ... ] ]14    SET TABLESPACE <em class="replaceable"><code>new_tablespace</code></em> [ NOWAIT ]15ALTER TABLE [ IF EXISTS ] <em class="replaceable"><code>name</code></em>16    ATTACH PARTITION <em class="replaceable"><code>partition_name</code></em> { FOR VALUES <em class="replaceable"><code>partition_bound_spec</code></em> | DEFAULT }17ALTER TABLE [ IF EXISTS ] <em class="replaceable"><code>name</code></em>18    DETACH PARTITION <em class="replaceable"><code>partition_name</code></em> [ CONCURRENTLY | FINALIZE ]19 20<span class="phrase">where <em class="replaceable"><code>action</code></em> is one of:</span>21 22    ADD [ COLUMN ] [ IF NOT EXISTS ] <em class="replaceable"><code>column_name</code></em> <em class="replaceable"><code>data_type</code></em> [ COLLATE <em class="replaceable"><code>collation</code></em> ] [ <em class="replaceable"><code>column_constraint</code></em> [ ... ] ]23    DROP [ COLUMN ] [ IF EXISTS ] <em class="replaceable"><code>column_name</code></em> [ RESTRICT | CASCADE ]24    ALTER [ COLUMN ] <em class="replaceable"><code>column_name</code></em> [ SET DATA ] TYPE <em class="replaceable"><code>data_type</code></em> [ COLLATE <em class="replaceable"><code>collation</code></em> ] [ USING <em class="replaceable"><code>expression</code></em> ]25    ALTER [ COLUMN ] <em class="replaceable"><code>column_name</code></em> SET DEFAULT <em class="replaceable"><code>expression</code></em>26    ALTER [ COLUMN ] <em class="replaceable"><code>column_name</code></em> DROP DEFAULT27    ALTER [ COLUMN ] <em class="replaceable"><code>column_name</code></em> { SET | DROP } NOT NULL28    ALTER [ COLUMN ] <em class="replaceable"><code>column_name</code></em> DROP EXPRESSION [ IF EXISTS ]29    ALTER [ COLUMN ] <em class="replaceable"><code>column_name</code></em> ADD GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( <em class="replaceable"><code>sequence_options</code></em> ) ]30    ALTER [ COLUMN ] <em class="replaceable"><code>column_name</code></em> { SET GENERATED { ALWAYS | BY DEFAULT } | SET <em class="replaceable"><code>sequence_option</code></em> | RESTART [ [ WITH ] <em class="replaceable"><code>restart</code></em> ] } [...]31    ALTER [ COLUMN ] <em class="replaceable"><code>column_name</code></em> DROP IDENTITY [ IF EXISTS ]32    ALTER [ COLUMN ] <em class="replaceable"><code>column_name</code></em> SET STATISTICS <em class="replaceable"><code>integer</code></em>33    ALTER [ COLUMN ] <em class="replaceable"><code>column_name</code></em> SET ( <em class="replaceable"><code>attribute_option</code></em> = <em class="replaceable"><code>value</code></em> [, ... ] )34    ALTER [ COLUMN ] <em class="replaceable"><code>column_name</code></em> RESET ( <em class="replaceable"><code>attribute_option</code></em> [, ... ] )35    ALTER [ COLUMN ] <em class="replaceable"><code>column_name</code></em> SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN | DEFAULT }36    ALTER [ COLUMN ] <em class="replaceable"><code>column_name</code></em> SET COMPRESSION <em class="replaceable"><code>compression_method</code></em>37    ADD <em class="replaceable"><code>table_constraint</code></em> [ NOT VALID ]38    ADD <em class="replaceable"><code>table_constraint_using_index</code></em>39    ALTER CONSTRAINT <em class="replaceable"><code>constraint_name</code></em> [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]40    VALIDATE CONSTRAINT <em class="replaceable"><code>constraint_name</code></em>41    DROP CONSTRAINT [ IF EXISTS ]  <em class="replaceable"><code>constraint_name</code></em> [ RESTRICT | CASCADE ]42    DISABLE TRIGGER [ <em class="replaceable"><code>trigger_name</code></em> | ALL | USER ]43    ENABLE TRIGGER [ <em class="replaceable"><code>trigger_name</code></em> | ALL | USER ]44    ENABLE REPLICA TRIGGER <em class="replaceable"><code>trigger_name</code></em>45    ENABLE ALWAYS TRIGGER <em class="replaceable"><code>trigger_name</code></em>46    DISABLE RULE <em class="replaceable"><code>rewrite_rule_name</code></em>47    ENABLE RULE <em class="replaceable"><code>rewrite_rule_name</code></em>48    ENABLE REPLICA RULE <em class="replaceable"><code>rewrite_rule_name</code></em>49    ENABLE ALWAYS RULE <em class="replaceable"><code>rewrite_rule_name</code></em>50    DISABLE ROW LEVEL SECURITY51    ENABLE ROW LEVEL SECURITY52    FORCE ROW LEVEL SECURITY53    NO FORCE ROW LEVEL SECURITY54    CLUSTER ON <em class="replaceable"><code>index_name</code></em>55    SET WITHOUT CLUSTER56    SET WITHOUT OIDS57    SET ACCESS METHOD <em class="replaceable"><code>new_access_method</code></em>58    SET TABLESPACE <em class="replaceable"><code>new_tablespace</code></em>59    SET { LOGGED | UNLOGGED }60    SET ( <em class="replaceable"><code>storage_parameter</code></em> [= <em class="replaceable"><code>value</code></em>] [, ... ] )61    RESET ( <em class="replaceable"><code>storage_parameter</code></em> [, ... ] )62    INHERIT <em class="replaceable"><code>parent_table</code></em>63    NO INHERIT <em class="replaceable"><code>parent_table</code></em>64    OF <em class="replaceable"><code>type_name</code></em>65    NOT OF66    OWNER TO { <em class="replaceable"><code>new_owner</code></em> | CURRENT_ROLE | CURRENT_USER | SESSION_USER }67    REPLICA IDENTITY { DEFAULT | USING INDEX <em class="replaceable"><code>index_name</code></em> | FULL | NOTHING }68 69<span class="phrase">and <em class="replaceable"><code>partition_bound_spec</code></em> is:</span>70 71IN ( <em class="replaceable"><code>partition_bound_expr</code></em> [, ...] ) |72FROM ( { <em class="replaceable"><code>partition_bound_expr</code></em> | MINVALUE | MAXVALUE } [, ...] )73  TO ( { <em class="replaceable"><code>partition_bound_expr</code></em> | MINVALUE | MAXVALUE } [, ...] ) |74WITH ( MODULUS <em class="replaceable"><code>numeric_literal</code></em>, REMAINDER <em class="replaceable"><code>numeric_literal</code></em> )75 76<span class="phrase">and <em class="replaceable"><code>column_constraint</code></em> is:</span>77 78[ CONSTRAINT <em class="replaceable"><code>constraint_name</code></em> ]79{ NOT NULL |80  NULL |81  CHECK ( <em class="replaceable"><code>expression</code></em> ) [ NO INHERIT ] |82  DEFAULT <em class="replaceable"><code>default_expr</code></em> |83  GENERATED ALWAYS AS ( <em class="replaceable"><code>generation_expr</code></em> ) STORED |84  GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( <em class="replaceable"><code>sequence_options</code></em> ) ] |85  UNIQUE [ NULLS [ NOT ] DISTINCT ] <em class="replaceable"><code>index_parameters</code></em> |86  PRIMARY KEY <em class="replaceable"><code>index_parameters</code></em> |87  REFERENCES <em class="replaceable"><code>reftable</code></em> [ ( <em class="replaceable"><code>refcolumn</code></em> ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ]88    [ ON DELETE <em class="replaceable"><code>referential_action</code></em> ] [ ON UPDATE <em class="replaceable"><code>referential_action</code></em> ] }89[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]90 91<span class="phrase">and <em class="replaceable"><code>table_constraint</code></em> is:</span>92 93[ CONSTRAINT <em class="replaceable"><code>constraint_name</code></em> ]94{ CHECK ( <em class="replaceable"><code>expression</code></em> ) [ NO INHERIT ] |95  UNIQUE [ NULLS [ NOT ] DISTINCT ] ( <em class="replaceable"><code>column_name</code></em> [, ... ] ) <em class="replaceable"><code>index_parameters</code></em> |96  PRIMARY KEY ( <em class="replaceable"><code>column_name</code></em> [, ... ] ) <em class="replaceable"><code>index_parameters</code></em> |97  EXCLUDE [ USING <em class="replaceable"><code>index_method</code></em> ] ( <em class="replaceable"><code>exclude_element</code></em> WITH <em class="replaceable"><code>operator</code></em> [, ... ] ) <em class="replaceable"><code>index_parameters</code></em> [ WHERE ( <em class="replaceable"><code>predicate</code></em> ) ] |98  FOREIGN KEY ( <em class="replaceable"><code>column_name</code></em> [, ... ] ) REFERENCES <em class="replaceable"><code>reftable</code></em> [ ( <em class="replaceable"><code>refcolumn</code></em> [, ... ] ) ]99    [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ] [ ON DELETE <em class="replaceable"><code>referential_action</code></em> ] [ ON UPDATE <em class="replaceable"><code>referential_action</code></em> ] }100[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]101 102<span class="phrase">and <em class="replaceable"><code>table_constraint_using_index</code></em> is:</span>103 104    [ CONSTRAINT <em class="replaceable"><code>constraint_name</code></em> ]105    { UNIQUE | PRIMARY KEY } USING INDEX <em class="replaceable"><code>index_name</code></em>106    [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]107 108<span class="phrase"><em class="replaceable"><code>index_parameters</code></em> in <code class="literal">UNIQUE</code>, <code class="literal">PRIMARY KEY</code>, and <code class="literal">EXCLUDE</code> constraints are:</span>109 110[ INCLUDE ( <em class="replaceable"><code>column_name</code></em> [, ... ] ) ]111[ WITH ( <em class="replaceable"><code>storage_parameter</code></em> [= <em class="replaceable"><code>value</code></em>] [, ... ] ) ]112[ USING INDEX TABLESPACE <em class="replaceable"><code>tablespace_name</code></em> ]113 114<span class="phrase"><em class="replaceable"><code>exclude_element</code></em> in an <code class="literal">EXCLUDE</code> constraint is:</span>115 116{ <em class="replaceable"><code>column_name</code></em> | ( <em class="replaceable"><code>expression</code></em> ) } [ COLLATE <em class="replaceable"><code>collation</code></em> ] [ <em class="replaceable"><code>opclass</code></em> [ ( <em class="replaceable"><code>opclass_parameter</code></em> = <em class="replaceable"><code>value</code></em> [, ... ] ) ] ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ]117 118<span class="phrase"><em class="replaceable"><code>referential_action</code></em> in a <code class="literal">FOREIGN KEY</code>/<code class="literal">REFERENCES</code> constraint is:</span>119 120{ NO ACTION | RESTRICT | CASCADE | SET NULL [ ( <em class="replaceable"><code>column_name</code></em> [, ... ] ) ] | SET DEFAULT [ ( <em class="replaceable"><code>column_name</code></em> [, ... ] ) ] }121</pre></div><div class="refsect1" id="id-1.9.3.35.5"><h2>Description</h2><p>122   <code class="command">ALTER TABLE</code> changes the definition of an existing table.123   There are several subforms described below. Note that the lock level required124   may differ for each subform. An <code class="literal">ACCESS EXCLUSIVE</code> lock is125   acquired unless explicitly noted. When multiple subcommands are given, the126   lock acquired will be the strictest one required by any subcommand.127 128  </p><div class="variablelist"><dl class="variablelist"><dt id="SQL-ALTERTABLE-DESC-ADD-COLUMN"><span class="term"><code class="literal">ADD COLUMN [ IF NOT EXISTS ]</code></span> <a href="#SQL-ALTERTABLE-DESC-ADD-COLUMN" class="id_link">#</a></dt><dd><p>129      This form adds a new column to the table, using the same syntax as130      <a class="link" href="sql-createtable.html" title="CREATE TABLE"><code class="command">CREATE TABLE</code></a>. If <code class="literal">IF NOT EXISTS</code>131      is specified and a column already exists with this name,132      no error is thrown.133     </p></dd><dt id="SQL-ALTERTABLE-DESC-DROP-COLUMN"><span class="term"><code class="literal">DROP COLUMN [ IF EXISTS ]</code></span> <a href="#SQL-ALTERTABLE-DESC-DROP-COLUMN" class="id_link">#</a></dt><dd><p>134      This form drops a column from a table.  Indexes and135      table constraints involving the column will be automatically136      dropped as well.137      Multivariate statistics referencing the dropped column will also be138      removed if the removal of the column would cause the statistics to139      contain data for only a single column.140      You will need to say <code class="literal">CASCADE</code> if anything outside the table141      depends on the column, for example, foreign key references or views.142      If <code class="literal">IF EXISTS</code> is specified and the column143      does not exist, no error is thrown. In this case a notice144      is issued instead.145     </p></dd><dt id="SQL-ALTERTABLE-DESC-SET-DATA-TYPE"><span class="term"><code class="literal">SET DATA TYPE</code></span> <a href="#SQL-ALTERTABLE-DESC-SET-DATA-TYPE" class="id_link">#</a></dt><dd><p>146      This form changes the type of a column of a table. Indexes and147      simple table constraints involving the column will be automatically148      converted to use the new column type by reparsing the originally149      supplied expression.150      The optional <code class="literal">COLLATE</code> clause specifies a collation151      for the new column; if omitted, the collation is the default for the152      new column type.153      The optional <code class="literal">USING</code>154      clause specifies how to compute the new column value from the old;155      if omitted, the default conversion is the same as an assignment156      cast from old data type to new.  A  <code class="literal">USING</code>157      clause must be provided if there is no implicit or assignment158      cast from old to new type.159     </p><p>160      When this form is used, the column's statistics are removed,161      so running <a class="link" href="sql-analyze.html" title="ANALYZE"><code class="command">ANALYZE</code></a>162      on the table afterwards is recommended.163     </p></dd><dt id="SQL-ALTERTABLE-DESC-SET-DROP-DEFAULT"><span class="term"><code class="literal">SET</code>/<code class="literal">DROP DEFAULT</code></span> <a href="#SQL-ALTERTABLE-DESC-SET-DROP-DEFAULT" class="id_link">#</a></dt><dd><p>164      These forms set or remove the default value for a column (where165      removal is equivalent to setting the default value to NULL).  The new166      default value will only apply in subsequent <code class="command">INSERT</code>167      or <code class="command">UPDATE</code> commands; it does not cause rows already168      in the table to change.169     </p></dd><dt id="SQL-ALTERTABLE-DESC-SET-DROP-NOT-NULL"><span class="term"><code class="literal">SET</code>/<code class="literal">DROP NOT NULL</code></span> <a href="#SQL-ALTERTABLE-DESC-SET-DROP-NOT-NULL" class="id_link">#</a></dt><dd><p>170      These forms change whether a column is marked to allow null171      values or to reject null values.172     </p><p>173      <code class="literal">SET NOT NULL</code> may only be applied to a column174      provided none of the records in the table contain a175      <code class="literal">NULL</code> value for the column.  Ordinarily this is176      checked during the <code class="literal">ALTER TABLE</code> by scanning the177      entire table; however, if a valid <code class="literal">CHECK</code> constraint is178      found which proves no <code class="literal">NULL</code> can exist, then the179      table scan is skipped.180     </p><p>181      If this table is a partition, one cannot perform <code class="literal">DROP NOT NULL</code>182      on a column if it is marked <code class="literal">NOT NULL</code> in the parent183      table.  To drop the <code class="literal">NOT NULL</code> constraint from all the184      partitions, perform <code class="literal">DROP NOT NULL</code> on the parent185      table.  Even if there is no <code class="literal">NOT NULL</code> constraint on the186      parent, such a constraint can still be added to individual partitions,187      if desired; that is, the children can disallow nulls even if the parent188      allows them, but not the other way around.189     </p></dd><dt id="SQL-ALTERTABLE-DESC-DROP-EXPRESSION"><span class="term"><code class="literal">DROP EXPRESSION [ IF EXISTS ]</code></span> <a href="#SQL-ALTERTABLE-DESC-DROP-EXPRESSION" class="id_link">#</a></dt><dd><p>190      This form turns a stored generated column into a normal base column.191      Existing data in the columns is retained, but future changes will no192      longer apply the generation expression.193     </p><p>194      If <code class="literal">DROP EXPRESSION IF EXISTS</code> is specified and the195      column is not a stored generated column, no error is thrown.  In this196      case a notice is issued instead.197     </p></dd><dt id="SQL-ALTERTABLE-DESC-GENERATED-IDENTITY"><span class="term"><code class="literal">ADD GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY</code><br /></span><span class="term"><code class="literal">SET GENERATED { ALWAYS | BY DEFAULT }</code><br /></span><span class="term"><code class="literal">DROP IDENTITY [ IF EXISTS ]</code></span> <a href="#SQL-ALTERTABLE-DESC-GENERATED-IDENTITY" class="id_link">#</a></dt><dd><p>198      These forms change whether a column is an identity column or change the199      generation attribute of an existing identity column.200      See <a class="link" href="sql-createtable.html" title="CREATE TABLE"><code class="command">CREATE TABLE</code></a> for details.201      Like <code class="literal">SET DEFAULT</code>, these forms only affect the202      behavior of subsequent <code class="command">INSERT</code>203      and <code class="command">UPDATE</code> commands; they do not cause rows204      already in the table to change.205     </p><p>206      If <code class="literal">DROP IDENTITY IF EXISTS</code> is specified and the207      column is not an identity column, no error is thrown.  In this case a208      notice is issued instead.209     </p></dd><dt id="SQL-ALTERTABLE-DESC-SET-SEQUENCE-OPTION"><span class="term"><code class="literal">SET <em class="replaceable"><code>sequence_option</code></em></code><br /></span><span class="term"><code class="literal">RESTART</code></span> <a href="#SQL-ALTERTABLE-DESC-SET-SEQUENCE-OPTION" class="id_link">#</a></dt><dd><p>210      These forms alter the sequence that underlies an existing identity211      column.  <em class="replaceable"><code>sequence_option</code></em> is an option212      supported by <a class="link" href="sql-altersequence.html" title="ALTER SEQUENCE"><code class="command">ALTER SEQUENCE</code></a> such213      as <code class="literal">INCREMENT BY</code>.214     </p></dd><dt id="SQL-ALTERTABLE-DESC-SET-STATISTICS"><span class="term"><code class="literal">SET STATISTICS</code></span> <a href="#SQL-ALTERTABLE-DESC-SET-STATISTICS" class="id_link">#</a></dt><dd><p>215      This form216      sets the per-column statistics-gathering target for subsequent217      <a class="link" href="sql-analyze.html" title="ANALYZE"><code class="command">ANALYZE</code></a> operations.218      The target can be set in the range 0 to 10000; alternatively, set it219      to -1 to revert to using the system default statistics220      target (<a class="xref" href="runtime-config-query.html#GUC-DEFAULT-STATISTICS-TARGET">default_statistics_target</a>).221      For more information on the use of statistics by the222      <span class="productname">PostgreSQL</span> query planner, refer to223      <a class="xref" href="planner-stats.html" title="14.2. Statistics Used by the Planner">Section 14.2</a>.224     </p><p>225      <code class="literal">SET STATISTICS</code> acquires a226      <code class="literal">SHARE UPDATE EXCLUSIVE</code> lock.227     </p></dd><dt id="SQL-ALTERTABLE-DESC-SET-ATTRIBUTE-OPTION"><span class="term"><code class="literal">SET ( <em class="replaceable"><code>attribute_option</code></em> = <em class="replaceable"><code>value</code></em> [, ... ] )</code><br /></span><span class="term"><code class="literal">RESET ( <em class="replaceable"><code>attribute_option</code></em> [, ... ] )</code></span> <a href="#SQL-ALTERTABLE-DESC-SET-ATTRIBUTE-OPTION" class="id_link">#</a></dt><dd><p>228      This form sets or resets per-attribute options.  Currently, the only229      defined per-attribute options are <code class="literal">n_distinct</code> and230      <code class="literal">n_distinct_inherited</code>, which override the231      number-of-distinct-values estimates made by subsequent232      <a class="link" href="sql-analyze.html" title="ANALYZE"><code class="command">ANALYZE</code></a>233      operations.  <code class="literal">n_distinct</code> affects the statistics for the table234      itself, while <code class="literal">n_distinct_inherited</code> affects the statistics235      gathered for the table plus its inheritance children.  When set to a236      positive value, <code class="command">ANALYZE</code> will assume that the column contains237      exactly the specified number of distinct nonnull values.  When set to a238      negative value, which must be greater239      than or equal to -1, <code class="command">ANALYZE</code> will assume that the number of240      distinct nonnull values in the column is linear in the size of the241      table; the exact count is to be computed by multiplying the estimated242      table size by the absolute value of the given number.  For example,243      a value of -1 implies that all values in the column are distinct, while244      a value of -0.5 implies that each value appears twice on the average.245      This can be useful when the size of the table changes over time, since246      the multiplication by the number of rows in the table is not performed247      until query planning time.  Specify a value of 0 to revert to estimating248      the number of distinct values normally.  For more information on the use249      of statistics by the <span class="productname">PostgreSQL</span> query250      planner, refer to <a class="xref" href="planner-stats.html" title="14.2. Statistics Used by the Planner">Section 14.2</a>.251     </p><p>252      Changing per-attribute options acquires a253      <code class="literal">SHARE UPDATE EXCLUSIVE</code> lock.254     </p></dd><dt id="SQL-ALTERTABLE-DESC-SET-STORAGE"><span class="term">255     <code class="literal">SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN | DEFAULT }</code>256     <a id="id-1.9.3.35.5.2.3.11.1.2" class="indexterm"></a>257    </span> <a href="#SQL-ALTERTABLE-DESC-SET-STORAGE" class="id_link">#</a></dt><dd><p>258      This form sets the storage mode for a column. This controls whether this259      column is held inline or in a secondary <acronym class="acronym">TOAST</acronym> table,260      and whether the data261      should be compressed or not. <code class="literal">PLAIN</code> must be used262      for fixed-length values such as <code class="type">integer</code> and is263      inline, uncompressed. <code class="literal">MAIN</code> is for inline,264      compressible data. <code class="literal">EXTERNAL</code> is for external,265      uncompressed data, and <code class="literal">EXTENDED</code> is for external,266      compressed data.267      Writing <code class="literal">DEFAULT</code> sets the storage mode to the default268      mode for the column's data type.  <code class="literal">EXTENDED</code> is the269      default for most data types that support non-<code class="literal">PLAIN</code>270      storage.271      Use of <code class="literal">EXTERNAL</code> will make substring operations on272      very large <code class="type">text</code> and <code class="type">bytea</code> values run faster,273      at the penalty of increased storage space.274      Note that <code class="literal">ALTER TABLE ... SET STORAGE</code> doesn't itself275      change anything in the table; it just sets the strategy to be pursued276      during future table updates.277      See <a class="xref" href="storage-toast.html" title="73.2. TOAST">Section 73.2</a> for more information.278     </p></dd><dt id="SQL-ALTERTABLE-DESC-SET-COMPRESSION"><span class="term">279     <code class="literal">SET COMPRESSION <em class="replaceable"><code>compression_method</code></em></code>280    </span> <a href="#SQL-ALTERTABLE-DESC-SET-COMPRESSION" class="id_link">#</a></dt><dd><p>281      This form sets the compression method for a column, determining how282      values inserted in future will be compressed (if the storage mode283      permits compression at all).284      This does not cause the table to be rewritten, so existing data may still285      be compressed with other compression methods.  If the table is restored286      with <span class="application">pg_restore</span>, then all values are rewritten287      with the configured compression method.288      However, when data is inserted from another relation (for example,289      by <code class="command">INSERT ... SELECT</code>), values from the source table are290      not necessarily detoasted, so any previously compressed data may retain291      its existing compression method, rather than being recompressed with the292      compression method of the target column.293      The supported compression294      methods are <code class="literal">pglz</code> and <code class="literal">lz4</code>.295      (<code class="literal">lz4</code> is available only if <code class="option">--with-lz4</code>296      was used when building <span class="productname">PostgreSQL</span>.)  In297      addition, <em class="replaceable"><code>compression_method</code></em>298      can be <code class="literal">default</code>, which selects the default behavior of299      consulting the <a class="xref" href="runtime-config-client.html#GUC-DEFAULT-TOAST-COMPRESSION">default_toast_compression</a> setting300      at the time of data insertion to determine the method to use.301     </p></dd><dt id="SQL-ALTERTABLE-DESC-ADD-TABLE-CONSTRAINT"><span class="term"><code class="literal">ADD <em class="replaceable"><code>table_constraint</code></em> [ NOT VALID ]</code></span> <a href="#SQL-ALTERTABLE-DESC-ADD-TABLE-CONSTRAINT" class="id_link">#</a></dt><dd><p>302      This form adds a new constraint to a table using the same constraint303      syntax as <a class="link" href="sql-createtable.html" title="CREATE TABLE"><code class="command">CREATE TABLE</code></a>, plus the option <code class="literal">NOT304      VALID</code>, which is currently only allowed for foreign key305      and CHECK constraints.306     </p><p>307      Normally, this form will cause a scan of the table to verify that all308      existing rows in the table satisfy the new constraint.  But if309      the <code class="literal">NOT VALID</code> option is used, this310      potentially-lengthy scan is skipped.  The constraint will still be311      enforced against subsequent inserts or updates (that is, they'll fail312      unless there is a matching row in the referenced table, in the case313      of foreign keys, or they'll fail unless the new row matches the314      specified check condition).  But the315      database will not assume that the constraint holds for all rows in316      the table, until it is validated by using the <code class="literal">VALIDATE317      CONSTRAINT</code> option.318      See <a class="xref" href="sql-altertable.html#SQL-ALTERTABLE-NOTES" title="Notes">Notes</a> below for more information319      about using the <code class="literal">NOT VALID</code> option.320     </p><p>321      Although most forms of <code class="literal">ADD322      <em class="replaceable"><code>table_constraint</code></em></code>323      require an <code class="literal">ACCESS EXCLUSIVE</code> lock, <code class="literal">ADD324      FOREIGN KEY</code> requires only a <code class="literal">SHARE ROW325      EXCLUSIVE</code> lock.  Note that <code class="literal">ADD FOREIGN KEY</code>326      also acquires a <code class="literal">SHARE ROW EXCLUSIVE</code> lock on the327      referenced table, in addition to the lock on the table on which the328      constraint is declared.329     </p><p>330      Additional restrictions apply when unique or primary key constraints331      are added to partitioned tables; see <a class="link" href="sql-createtable.html" title="CREATE TABLE"><code class="command">CREATE TABLE</code></a>.332      Also, foreign key constraints on partitioned333      tables may not be declared <code class="literal">NOT VALID</code> at present.334     </p></dd><dt id="SQL-ALTERTABLE-DESC-ADD-TABLE-CONSTRAINT-USING-INDEX"><span class="term"><code class="literal">ADD <em class="replaceable"><code>table_constraint_using_index</code></em></code></span> <a href="#SQL-ALTERTABLE-DESC-ADD-TABLE-CONSTRAINT-USING-INDEX" class="id_link">#</a></dt><dd><p>335      This form adds a new <code class="literal">PRIMARY KEY</code> or <code class="literal">UNIQUE</code>336      constraint to a table based on an existing unique index.  All the337      columns of the index will be included in the constraint.338     </p><p>339      The index cannot have expression columns nor be a partial index.340      Also, it must be a b-tree index with default sort ordering.  These341      restrictions ensure that the index is equivalent to one that would be342      built by a regular <code class="literal">ADD PRIMARY KEY</code> or <code class="literal">ADD UNIQUE</code>343      command.344     </p><p>345      If <code class="literal">PRIMARY KEY</code> is specified, and the index's columns are not346      already marked <code class="literal">NOT NULL</code>, then this command will attempt to347      do <code class="literal">ALTER COLUMN SET NOT NULL</code> against each such column.348      That requires a full table scan to verify the column(s) contain no349      nulls.  In all other cases, this is a fast operation.350     </p><p>351      If a constraint name is provided then the index will be renamed to match352      the constraint name.  Otherwise the constraint will be named the same as353      the index.354     </p><p>355      After this command is executed, the index is <span class="quote">“<span class="quote">owned</span>”</span> by the356      constraint, in the same way as if the index had been built by357      a regular <code class="literal">ADD PRIMARY KEY</code> or <code class="literal">ADD UNIQUE</code>358      command.  In particular, dropping the constraint will make the index359      disappear too.360     </p><p>361      This form is not currently supported on partitioned tables.362     </p><div class="note"><h3 class="title">Note</h3><p>363       Adding a constraint using an existing index can be helpful in364       situations where a new constraint needs to be added without blocking365       table updates for a long time.  To do that, create the index using366       <code class="command">CREATE INDEX CONCURRENTLY</code>, and then install it as an367       official constraint using this syntax.  See the example below.368      </p></div></dd><dt id="SQL-ALTERTABLE-DESC-ALTER-CONSTRAINT"><span class="term"><code class="literal">ALTER CONSTRAINT</code></span> <a href="#SQL-ALTERTABLE-DESC-ALTER-CONSTRAINT" class="id_link">#</a></dt><dd><p>369      This form alters the attributes of a constraint that was previously370      created. Currently only foreign key constraints may be altered.371     </p></dd><dt id="SQL-ALTERTABLE-DESC-VALIDATE-CONSTRAINT"><span class="term"><code class="literal">VALIDATE CONSTRAINT</code></span> <a href="#SQL-ALTERTABLE-DESC-VALIDATE-CONSTRAINT" class="id_link">#</a></dt><dd><p>372      This form validates a foreign key or check constraint that was373      previously created as <code class="literal">NOT VALID</code>, by scanning the374      table to ensure there are no rows for which the constraint is not375      satisfied.  Nothing happens if the constraint is already marked valid.376      (See <a class="xref" href="sql-altertable.html#SQL-ALTERTABLE-NOTES" title="Notes">Notes</a> below for an explanation377      of the usefulness of this command.)378     </p><p>379      This command acquires a <code class="literal">SHARE UPDATE EXCLUSIVE</code> lock.380     </p></dd><dt id="SQL-ALTERTABLE-DESC-DROP-CONSTRAINT"><span class="term"><code class="literal">DROP CONSTRAINT [ IF EXISTS ]</code></span> <a href="#SQL-ALTERTABLE-DESC-DROP-CONSTRAINT" class="id_link">#</a></dt><dd><p>381      This form drops the specified constraint on a table, along with382      any index underlying the constraint.383      If <code class="literal">IF EXISTS</code> is specified and the constraint384      does not exist, no error is thrown. In this case a notice is issued instead.385     </p></dd><dt id="SQL-ALTERTABLE-DESC-DISABLE-ENABLE-TRIGGER"><span class="term"><code class="literal">DISABLE</code>/<code class="literal">ENABLE [ REPLICA | ALWAYS ] TRIGGER</code></span> <a href="#SQL-ALTERTABLE-DESC-DISABLE-ENABLE-TRIGGER" class="id_link">#</a></dt><dd><p>386      These forms configure the firing of trigger(s) belonging to the table.387      A disabled trigger is still known to the system, but is not executed388      when its triggering event occurs.  (For a deferred trigger, the enable389      status is checked when the event occurs, not when the trigger function390      is actually executed.)  One can disable or enable a single391      trigger specified by name, or all triggers on the table, or only392      user triggers (this option excludes internally generated constraint393      triggers, such as those that are used to implement foreign key394      constraints or deferrable uniqueness and exclusion constraints).395      Disabling or enabling internally generated constraint triggers396      requires superuser privileges; it should be done with caution since397      of course the integrity of the constraint cannot be guaranteed if the398      triggers are not executed.399     </p><p>400      The trigger firing mechanism is also affected by the configuration401      variable <a class="xref" href="runtime-config-client.html#GUC-SESSION-REPLICATION-ROLE">session_replication_role</a>. Simply enabled402      triggers (the default) will fire when the replication role is <span class="quote">“<span class="quote">origin</span>”</span>403      (the default) or <span class="quote">“<span class="quote">local</span>”</span>. Triggers configured as <code class="literal">ENABLE404      REPLICA</code> will only fire if the session is in <span class="quote">“<span class="quote">replica</span>”</span>405      mode, and triggers configured as <code class="literal">ENABLE ALWAYS</code> will406      fire regardless of the current replication role.407     </p><p>408      The effect of this mechanism is that in the default configuration,409      triggers do not fire on replicas.  This is useful because if a trigger410      is used on the origin to propagate data between tables, then the411      replication system will also replicate the propagated data; so the412      trigger should not fire a second time on the replica, because that would413      lead to duplication.  However, if a trigger is used for another purpose414      such as creating external alerts, then it might be appropriate to set it415      to <code class="literal">ENABLE ALWAYS</code> so that it is also fired on416      replicas.417     </p><p>418      When this command is applied to a partitioned table, the states of419      corresponding clone triggers in the partitions are updated too,420      unless <code class="literal">ONLY</code> is specified.421     </p><p>422      This command acquires a <code class="literal">SHARE ROW EXCLUSIVE</code> lock.423     </p></dd><dt id="SQL-ALTERTABLE-DESC-DISABLE-ENABLE-RULE"><span class="term"><code class="literal">DISABLE</code>/<code class="literal">ENABLE [ REPLICA | ALWAYS ] RULE</code></span> <a href="#SQL-ALTERTABLE-DESC-DISABLE-ENABLE-RULE" class="id_link">#</a></dt><dd><p>424      These forms configure the firing of rewrite rules belonging to the table.425      A disabled rule is still known to the system, but is not applied426      during query rewriting. The semantics are as for disabled/enabled427      triggers. This configuration is ignored for <code class="literal">ON SELECT</code> rules, which428      are always applied in order to keep views working even if the current429      session is in a non-default replication role.430     </p><p>431      The rule firing mechanism is also affected by the configuration variable432      <a class="xref" href="runtime-config-client.html#GUC-SESSION-REPLICATION-ROLE">session_replication_role</a>, analogous to triggers as433      described above.434     </p></dd><dt id="SQL-ALTERTABLE-DESC-DISABLE-ENABLE-ROW-LEVEL-SECURITY"><span class="term"><code class="literal">DISABLE</code>/<code class="literal">ENABLE ROW LEVEL SECURITY</code></span> <a href="#SQL-ALTERTABLE-DESC-DISABLE-ENABLE-ROW-LEVEL-SECURITY" class="id_link">#</a></dt><dd><p>435      These forms control the application of row security policies belonging436      to the table.  If enabled and no policies exist for the table, then a437      default-deny policy is applied.  Note that policies can exist for a table438      even if row-level security is disabled.  In this case, the policies will439      <span class="emphasis"><em>not</em></span> be applied and the policies will be ignored.440      See also441      <a class="link" href="sql-createpolicy.html" title="CREATE POLICY"><code class="command">CREATE POLICY</code></a>.442     </p></dd><dt id="SQL-ALTERTABLE-DESC-FORCE-ROW-LEVEL-SECURITY"><span class="term"><code class="literal">NO FORCE</code>/<code class="literal">FORCE ROW LEVEL SECURITY</code></span> <a href="#SQL-ALTERTABLE-DESC-FORCE-ROW-LEVEL-SECURITY" class="id_link">#</a></dt><dd><p>443      These forms control the application of row security policies belonging444      to the table when the user is the table owner.  If enabled, row-level445      security policies will be applied when the user is the table owner.  If446      disabled (the default) then row-level security will not be applied when447      the user is the table owner.448      See also449      <a class="link" href="sql-createpolicy.html" title="CREATE POLICY"><code class="command">CREATE POLICY</code></a>.450     </p></dd><dt id="SQL-ALTERTABLE-DESC-CLUSTER-ON"><span class="term"><code class="literal">CLUSTER ON</code></span> <a href="#SQL-ALTERTABLE-DESC-CLUSTER-ON" class="id_link">#</a></dt><dd><p>451      This form selects the default index for future452      <a class="link" href="sql-cluster.html" title="CLUSTER"><code class="command">CLUSTER</code></a>453      operations.  It does not actually re-cluster the table.454     </p><p>455      Changing cluster options acquires a <code class="literal">SHARE UPDATE EXCLUSIVE</code> lock.456     </p></dd><dt id="SQL-ALTERTABLE-DESC-SET-WITHOUT-CLUSTER"><span class="term"><code class="literal">SET WITHOUT CLUSTER</code></span> <a href="#SQL-ALTERTABLE-DESC-SET-WITHOUT-CLUSTER" class="id_link">#</a></dt><dd><p>457      This form removes the most recently used458      <a class="link" href="sql-cluster.html" title="CLUSTER"><code class="command">CLUSTER</code></a>459      index specification from the table.  This affects460      future cluster operations that don't specify an index.461     </p><p>462      Changing cluster options acquires a <code class="literal">SHARE UPDATE EXCLUSIVE</code> lock.463     </p></dd><dt id="SQL-ALTERTABLE-DESC-SET-WITHOUT-OIDS"><span class="term"><code class="literal">SET WITHOUT OIDS</code></span> <a href="#SQL-ALTERTABLE-DESC-SET-WITHOUT-OIDS" class="id_link">#</a></dt><dd><p>464      Backward-compatible syntax for removing the <code class="literal">oid</code>465      system column.  As <code class="literal">oid</code> system columns cannot be466      added anymore, this never has an effect.467     </p></dd><dt id="SQL-ALTERTABLE-DESC-SET-ACCESS-METHOD"><span class="term"><code class="literal">SET ACCESS METHOD</code></span> <a href="#SQL-ALTERTABLE-DESC-SET-ACCESS-METHOD" class="id_link">#</a></dt><dd><p>468      This form changes the access method of the table by rewriting it. See469      <a class="xref" href="tableam.html" title="Chapter 63. Table Access Method Interface Definition">Chapter 63</a> for more information.470     </p></dd><dt id="SQL-ALTERTABLE-DESC-SET-TABLESPACE"><span class="term"><code class="literal">SET TABLESPACE</code></span> <a href="#SQL-ALTERTABLE-DESC-SET-TABLESPACE" class="id_link">#</a></dt><dd><p>471      This form changes the table's tablespace to the specified tablespace and472      moves the data file(s) associated with the table to the new tablespace.473      Indexes on the table, if any, are not moved; but they can be moved474      separately with additional <code class="literal">SET TABLESPACE</code> commands.475      When applied to a partitioned table, nothing is moved, but any476      partitions created afterwards with477      <code class="command">CREATE TABLE PARTITION OF</code> will use that tablespace,478      unless overridden by a <code class="literal">TABLESPACE</code> clause.479     </p><p>480      All tables in the current database in a tablespace can be moved by using481      the <code class="literal">ALL IN TABLESPACE</code> form, which will lock all tables482      to be moved first and then move each one.  This form also supports483      <code class="literal">OWNED BY</code>, which will only move tables owned by the484      roles specified.  If the <code class="literal">NOWAIT</code> option is specified485      then the command will fail if it is unable to acquire all of the locks486      required immediately.  Note that system catalogs are not moved by this487      command; use <code class="command">ALTER DATABASE</code> or explicit488      <code class="command">ALTER TABLE</code> invocations instead if desired.  The489      <code class="literal">information_schema</code> relations are not considered part490      of the system catalogs and will be moved.491      See also492      <a class="link" href="sql-createtablespace.html" title="CREATE TABLESPACE"><code class="command">CREATE TABLESPACE</code></a>.493     </p></dd><dt id="SQL-ALTERTABLE-DESC-SET-LOGGED-UNLOGGED"><span class="term"><code class="literal">SET { LOGGED | UNLOGGED }</code></span> <a href="#SQL-ALTERTABLE-DESC-SET-LOGGED-UNLOGGED" class="id_link">#</a></dt><dd><p>494      This form changes the table from unlogged to logged or vice-versa495      (see <a class="xref" href="sql-createtable.html#SQL-CREATETABLE-UNLOGGED"><code class="literal">UNLOGGED</code></a>).  It cannot be applied496      to a temporary table.497     </p><p>498      This also changes the persistence of any sequences linked to the table499      (for identity or serial columns).  However, it is also possible to500      change the persistence of such sequences separately.501     </p></dd><dt id="SQL-ALTERTABLE-DESC-SET-STORAGE-PARAMETER"><span class="term"><code class="literal">SET ( <em class="replaceable"><code>storage_parameter</code></em> [= <em class="replaceable"><code>value</code></em>] [, ... ] )</code></span> <a href="#SQL-ALTERTABLE-DESC-SET-STORAGE-PARAMETER" class="id_link">#</a></dt><dd><p>502      This form changes one or more storage parameters for the table.  See503      <a class="xref" href="sql-createtable.html#SQL-CREATETABLE-STORAGE-PARAMETERS" title="Storage Parameters">Storage Parameters</a> in the504      <a class="link" href="sql-createtable.html" title="CREATE TABLE"><code class="command">CREATE TABLE</code></a> documentation505      for details on the available parameters.  Note that the table contents506      will not be modified immediately by this command; depending on the507      parameter you might need to rewrite the table to get the desired effects.508      That can be done with <a class="link" href="sql-vacuum.html" title="VACUUM"><code class="command">VACUUM509      FULL</code></a>, <a class="link" href="sql-cluster.html" title="CLUSTER"><code class="command">CLUSTER</code></a> or one of the forms510      of <code class="command">ALTER TABLE</code> that forces a table rewrite.511      For planner related parameters, changes will take effect from the next512      time the table is locked so currently executing queries will not be513      affected.514     </p><p>515      <code class="literal">SHARE UPDATE EXCLUSIVE</code> lock will be taken for516      fillfactor, toast and autovacuum storage parameters, as well as the517      planner parameter <code class="varname">parallel_workers</code>.518     </p></dd><dt id="SQL-ALTERTABLE-DESC-RESET-STORAGE-PARAMETER"><span class="term"><code class="literal">RESET ( <em class="replaceable"><code>storage_parameter</code></em> [, ... ] )</code></span> <a href="#SQL-ALTERTABLE-DESC-RESET-STORAGE-PARAMETER" class="id_link">#</a></dt><dd><p>519      This form resets one or more storage parameters to their520      defaults.  As with <code class="literal">SET</code>, a table rewrite might be521      needed to update the table entirely.522     </p></dd><dt id="SQL-ALTERTABLE-DESC-INHERIT"><span class="term"><code class="literal">INHERIT <em class="replaceable"><code>parent_table</code></em></code></span> <a href="#SQL-ALTERTABLE-DESC-INHERIT" class="id_link">#</a></dt><dd><p>523      This form adds the target table as a new child of the specified parent524      table.  Subsequently, queries against the parent will include records525      of the target table.  To be added as a child, the target table must526      already contain all the same columns as the parent (it could have527      additional columns, too).  The columns must have matching data types,528      and if they have <code class="literal">NOT NULL</code> constraints in the parent529      then they must also have <code class="literal">NOT NULL</code> constraints in the530      child.531     </p><p>532      There must also be matching child-table constraints for all533      <code class="literal">CHECK</code> constraints of the parent, except those534      marked non-inheritable (that is, created with <code class="literal">ALTER TABLE ... ADD CONSTRAINT ... NO INHERIT</code>)535      in the parent, which are ignored; all child-table constraints matched536      must not be marked non-inheritable.537      Currently538      <code class="literal">UNIQUE</code>, <code class="literal">PRIMARY KEY</code>, and539      <code class="literal">FOREIGN KEY</code> constraints are not considered, but540      this might change in the future.541     </p></dd><dt id="SQL-ALTERTABLE-DESC-NO-INHERIT"><span class="term"><code class="literal">NO INHERIT <em class="replaceable"><code>parent_table</code></em></code></span> <a href="#SQL-ALTERTABLE-DESC-NO-INHERIT" class="id_link">#</a></dt><dd><p>542      This form removes the target table from the list of children of the543      specified parent table.544      Queries against the parent table will no longer include records drawn545      from the target table.546     </p></dd><dt id="SQL-ALTERTABLE-DESC-OF"><span class="term"><code class="literal">OF <em class="replaceable"><code>type_name</code></em></code></span> <a href="#SQL-ALTERTABLE-DESC-OF" class="id_link">#</a></dt><dd><p>547      This form links the table to a composite type as though <code class="command">CREATE548      TABLE OF</code> had formed it.  The table's list of column names and types549      must precisely match that of the composite type.  The table must550      not inherit from any other table.  These restrictions ensure551      that <code class="command">CREATE TABLE OF</code> would permit an equivalent table552      definition.553     </p></dd><dt id="SQL-ALTERTABLE-DESC-NOT-OF"><span class="term"><code class="literal">NOT OF</code></span> <a href="#SQL-ALTERTABLE-DESC-NOT-OF" class="id_link">#</a></dt><dd><p>554      This form dissociates a typed table from its type.555     </p></dd><dt id="SQL-ALTERTABLE-DESC-OWNER-TO"><span class="term"><code class="literal">OWNER TO</code></span> <a href="#SQL-ALTERTABLE-DESC-OWNER-TO" class="id_link">#</a></dt><dd><p>556      This form changes the owner of the table, sequence, view, materialized view,557      or foreign table to the specified user.558     </p></dd><dt id="SQL-ALTERTABLE-REPLICA-IDENTITY"><span class="term"><code class="literal">REPLICA IDENTITY</code></span> <a href="#SQL-ALTERTABLE-REPLICA-IDENTITY" class="id_link">#</a></dt><dd><p>559      This form changes the information which is written to the write-ahead log560      to identify rows which are updated or deleted.561      In most cases, the old value of each column is only logged if it differs562      from the new value; however, if the old value is stored externally, it is563      always logged regardless of whether it changed.564      This option has no effect except when logical replication is in use.565     </p><div class="variablelist"><dl class="variablelist"><dt id="SQL-ALTERTABLE-REPLICA-IDENTITY-DEFAULT"><span class="term"><code class="literal">DEFAULT</code></span> <a href="#SQL-ALTERTABLE-REPLICA-IDENTITY-DEFAULT" class="id_link">#</a></dt><dd><p>566         Records the old values of the columns of the primary key, if any.567         This is the default for non-system tables.568        </p></dd><dt id="SQL-ALTERTABLE-REPLICA-IDENTITY-USING-INDEX"><span class="term"><code class="literal">USING INDEX <em class="replaceable"><code>index_name</code></em></code></span> <a href="#SQL-ALTERTABLE-REPLICA-IDENTITY-USING-INDEX" class="id_link">#</a></dt><dd><p>569         Records the old values of the columns covered by the named index,570         that must be unique, not partial, not deferrable, and include only571         columns marked <code class="literal">NOT NULL</code>. If this index is572         dropped, the behavior is the same as <code class="literal">NOTHING</code>.573        </p></dd><dt id="SQL-ALTERTABLE-REPLICA-IDENTITY-FULL"><span class="term"><code class="literal">FULL</code></span> <a href="#SQL-ALTERTABLE-REPLICA-IDENTITY-FULL" class="id_link">#</a></dt><dd><p>574         Records the old values of all columns in the row.575        </p></dd><dt id="SQL-ALTERTABLE-REPLICA-IDENTITY-NOTHING"><span class="term"><code class="literal">NOTHING</code></span> <a href="#SQL-ALTERTABLE-REPLICA-IDENTITY-NOTHING" class="id_link">#</a></dt><dd><p>576         Records no information about the old row. This is the default for577         system tables.578        </p></dd></dl></div></dd><dt id="SQL-ALTERTABLE-DESC-RENAME"><span class="term"><code class="literal">RENAME</code></span> <a href="#SQL-ALTERTABLE-DESC-RENAME" class="id_link">#</a></dt><dd><p>579      The <code class="literal">RENAME</code> forms change the name of a table580      (or an index, sequence, view, materialized view, or foreign table), the581      name of an individual column in a table, or the name of a constraint of582      the table.  When renaming a constraint that has an underlying index,583      the index is renamed as well.584      There is no effect on the stored data.585     </p></dd><dt id="SQL-ALTERTABLE-DESC-SET-SCHEMA"><span class="term"><code class="literal">SET SCHEMA</code></span> <a href="#SQL-ALTERTABLE-DESC-SET-SCHEMA" class="id_link">#</a></dt><dd><p>586      This form moves the table into another schema.  Associated indexes,587      constraints, and sequences owned by table columns are moved as well.588     </p></dd><dt id="SQL-ALTERTABLE-ATTACH-PARTITION"><span class="term"><code class="literal">ATTACH PARTITION <em class="replaceable"><code>partition_name</code></em> { FOR VALUES <em class="replaceable"><code>partition_bound_spec</code></em> | DEFAULT }</code></span> <a href="#SQL-ALTERTABLE-ATTACH-PARTITION" class="id_link">#</a></dt><dd><p>589      This form attaches an existing table (which might itself be partitioned)590      as a partition of the target table. The table can be attached591      as a partition for specific values using <code class="literal">FOR VALUES</code>592      or as a default partition by using <code class="literal">DEFAULT</code>.593      For each index in the target table, a corresponding594      one will be created in the attached table; or, if an equivalent595      index already exists, it will be attached to the target table's index,596      as if <code class="command">ALTER INDEX ATTACH PARTITION</code> had been executed.597      Note that if the existing table is a foreign table, it is currently not598      allowed to attach the table as a partition of the target table if there599      are <code class="literal">UNIQUE</code> indexes on the target table.  (See also600      <a class="xref" href="sql-createforeigntable.html" title="CREATE FOREIGN TABLE"><span class="refentrytitle">CREATE FOREIGN TABLE</span></a>.)  For each user-defined601      row-level trigger that exists in the target table, a corresponding one602      is created in the attached table.603     </p><p>604      A partition using <code class="literal">FOR VALUES</code> uses same syntax for605      <em class="replaceable"><code>partition_bound_spec</code></em> as606      <a class="link" href="sql-createtable.html" title="CREATE TABLE"><code class="command">CREATE TABLE</code></a>.  The partition bound specification607      must correspond to the partitioning strategy and partition key of the608      target table.  The table to be attached must have all the same columns609      as the target table and no more; moreover, the column types must also610      match.  Also, it must have all the <code class="literal">NOT NULL</code> and611      <code class="literal">CHECK</code> constraints of the target table.  Currently612      <code class="literal">FOREIGN KEY</code> constraints are not considered.613      <code class="literal">UNIQUE</code> and <code class="literal">PRIMARY KEY</code> constraints614      from the parent table will be created in the partition, if they don't615      already exist.616      If any of the <code class="literal">CHECK</code> constraints of the table being617      attached are marked <code class="literal">NO INHERIT</code>, the command will fail;618      such constraints must be recreated without the619      <code class="literal">NO INHERIT</code> clause.620     </p><p>621      If the new partition is a regular table, a full table scan is performed622      to check that existing rows in the table do not violate the partition623      constraint. It is possible to avoid this scan by adding a valid624      <code class="literal">CHECK</code> constraint to the table that allows only625      rows satisfying the desired partition constraint before running this626      command. The <code class="literal">CHECK</code> constraint will be used to627      determine that the table need not be scanned to validate the partition628      constraint. This does not work, however, if any of the partition keys629      is an expression and the partition does not accept630      <code class="literal">NULL</code> values. If attaching a list partition that will631      not accept <code class="literal">NULL</code> values, also add a632      <code class="literal">NOT NULL</code> constraint to the partition key column,633      unless it's an expression.634     </p><p>635      If the new partition is a foreign table, nothing is done to verify636      that all the rows in the foreign table obey the partition constraint.637      (See the discussion in <a class="xref" href="sql-createforeigntable.html" title="CREATE FOREIGN TABLE"><span class="refentrytitle">CREATE FOREIGN TABLE</span></a> about638      constraints on the foreign table.)639     </p><p>640      When a table has a default partition, defining a new partition changes641      the partition constraint for the default partition. The default642      partition can't contain any rows that would need to be moved to the new643      partition, and will be scanned to verify that none are present. This644      scan, like the scan of the new partition, can be avoided if an645      appropriate <code class="literal">CHECK</code> constraint is present. Also like646      the scan of the new partition, it is always skipped when the default647      partition is a foreign table.648     </p><p>649      Attaching a partition acquires a650      <code class="literal">SHARE UPDATE EXCLUSIVE</code> lock on the parent table,651      in addition to the <code class="literal">ACCESS EXCLUSIVE</code> locks on the table652      being attached and on the default partition (if any).653     </p><p>654      Further locks must also be held on all sub-partitions if the table being655      attached is itself a partitioned table.  Likewise if the default656      partition is itself a partitioned table.  The locking of the657      sub-partitions can be avoided by adding a <code class="literal">CHECK</code>658      constraint as described in659      <a class="xref" href="ddl-partitioning.html#DDL-PARTITIONING-DECLARATIVE-MAINTENANCE" title="5.11.2.2. Partition Maintenance">Section 5.11.2.2</a>.660     </p></dd><dt id="SQL-ALTERTABLE-DETACH-PARTITION"><span class="term"><code class="literal">DETACH PARTITION <em class="replaceable"><code>partition_name</code></em> [ CONCURRENTLY | FINALIZE ]</code></span> <a href="#SQL-ALTERTABLE-DETACH-PARTITION" class="id_link">#</a></dt><dd><p>661      This form detaches the specified partition of the target table.  The detached662      partition continues to exist as a standalone table, but no longer has any663      ties to the table from which it was detached.  Any indexes that were664      attached to the target table's indexes are detached.  Any triggers that665      were created as clones of those in the target table are removed.666      <code class="literal">SHARE</code> lock is obtained on any tables that reference667      this partitioned table in foreign key constraints.668     </p><p>669      If <code class="literal">CONCURRENTLY</code> is specified, it runs using a reduced670      lock level to avoid blocking other sessions that might be accessing the671      partitioned table.  In this mode, two transactions are used internally.672      During the first transaction, a <code class="literal">SHARE UPDATE EXCLUSIVE</code>673      lock is taken on both parent table and partition, and the partition is674      marked as undergoing detach; at that point, the transaction is committed675      and all other transactions using the partitioned table are waited for.676      Once all those transactions have completed, the second transaction677      acquires <code class="literal">SHARE UPDATE EXCLUSIVE</code> on the partitioned678      table and <code class="literal">ACCESS EXCLUSIVE</code> on the partition,679      and the detach process completes.  A <code class="literal">CHECK</code> constraint680      that duplicates the partition constraint is added to the partition.681      <code class="literal">CONCURRENTLY</code> cannot be run in a transaction block and682      is not allowed if the partitioned table contains a default partition.683     </p><p>684      If <code class="literal">FINALIZE</code> is specified, a previous685      <code class="literal">DETACH CONCURRENTLY</code> invocation that was canceled or686      interrupted is completed.687      At most one partition in a partitioned table can be pending detach at688      a time.689     </p></dd></dl></div><p>690  </p><p>691   All the forms of ALTER TABLE that act on a single table, except692   <code class="literal">RENAME</code>, <code class="literal">SET SCHEMA</code>,693   <code class="literal">ATTACH PARTITION</code>, and694   <code class="literal">DETACH PARTITION</code> can be combined into695   a list of multiple alterations to be applied together.  For example, it696   is possible to add several columns and/or alter the type of several697   columns in a single command.  This is particularly useful with large698   tables, since only one pass over the table need be made.699  </p><p>700   You must own the table to use <code class="command">ALTER TABLE</code>.701   To change the schema or tablespace of a table, you must also have702   <code class="literal">CREATE</code> privilege on the new schema or tablespace.703   To add the table as a new child of a parent table, you must own the parent704   table as well.  Also, to attach a table as a new partition of the table,705   you must own the table being attached.706   To alter the owner, you must be able to <code class="literal">SET ROLE</code> to the707   new owning role, and that role must have <code class="literal">CREATE</code>708   privilege on the table's schema.709   (These restrictions enforce that altering the owner710   doesn't do anything you couldn't do by dropping and recreating the table.711   However, a superuser can alter ownership of any table anyway.)712   To add a column or alter a column type or use the <code class="literal">OF</code>713   clause, you must also have <code class="literal">USAGE</code> privilege on the data714   type.715  </p></div><div class="refsect1" id="id-1.9.3.35.6"><h2>Parameters</h2><div class="variablelist"><dl class="variablelist"><dt id="SQL-ALTERTABLE-PARMS-IF-EXISTS"><span class="term"><code class="literal">IF EXISTS</code></span> <a href="#SQL-ALTERTABLE-PARMS-IF-EXISTS" class="id_link">#</a></dt><dd><p>716        Do not throw an error if the table does not exist. A notice is issued717        in this case.718       </p></dd><dt id="SQL-ALTERTABLE-PARMS-NAME"><span class="term"><em class="replaceable"><code>name</code></em></span> <a href="#SQL-ALTERTABLE-PARMS-NAME" class="id_link">#</a></dt><dd><p>719        The name (optionally schema-qualified) of an existing table to720        alter. If <code class="literal">ONLY</code> is specified before the table name, only721        that table is altered. If <code class="literal">ONLY</code> is not specified, the table722        and all its descendant tables (if any) are altered.  Optionally,723        <code class="literal">*</code> can be specified after the table name to explicitly724        indicate that descendant tables are included.725       </p></dd><dt id="SQL-ALTERTABLE-PARMS-COLUMN-NAME"><span class="term"><em class="replaceable"><code>column_name</code></em></span> <a href="#SQL-ALTERTABLE-PARMS-COLUMN-NAME" class="id_link">#</a></dt><dd><p>726        Name of a new or existing column.727       </p></dd><dt id="SQL-ALTERTABLE-PARMS-NEW-COLUMN-NAME"><span class="term"><em class="replaceable"><code>new_column_name</code></em></span> <a href="#SQL-ALTERTABLE-PARMS-NEW-COLUMN-NAME" class="id_link">#</a></dt><dd><p>728        New name for an existing column.729       </p></dd><dt id="SQL-ALTERTABLE-PARMS-NEW-NAME"><span class="term"><em class="replaceable"><code>new_name</code></em></span> <a href="#SQL-ALTERTABLE-PARMS-NEW-NAME" class="id_link">#</a></dt><dd><p>730        New name for the table.731       </p></dd><dt id="SQL-ALTERTABLE-PARMS-DATA-TYPE"><span class="term"><em class="replaceable"><code>data_type</code></em></span> <a href="#SQL-ALTERTABLE-PARMS-DATA-TYPE" class="id_link">#</a></dt><dd><p>732        Data type of the new column, or new data type for an existing733        column.734       </p></dd><dt id="SQL-ALTERTABLE-PARMS-TABLE-CONSTRAINT"><span class="term"><em class="replaceable"><code>table_constraint</code></em></span> <a href="#SQL-ALTERTABLE-PARMS-TABLE-CONSTRAINT" class="id_link">#</a></dt><dd><p>735        New table constraint for the table.736       </p></dd><dt id="SQL-ALTERTABLE-PARMS-CONSTRAINT-NAME"><span class="term"><em class="replaceable"><code>constraint_name</code></em></span> <a href="#SQL-ALTERTABLE-PARMS-CONSTRAINT-NAME" class="id_link">#</a></dt><dd><p>737        Name of a new or existing constraint.738       </p></dd><dt id="SQL-ALTERTABLE-PARMS-CASCADE"><span class="term"><code class="literal">CASCADE</code></span> <a href="#SQL-ALTERTABLE-PARMS-CASCADE" class="id_link">#</a></dt><dd><p>739        Automatically drop objects that depend on the dropped column740        or constraint (for example, views referencing the column),741        and in turn all objects that depend on those objects742        (see <a class="xref" href="ddl-depend.html" title="5.14. Dependency Tracking">Section 5.14</a>).743       </p></dd><dt id="SQL-ALTERTABLE-PARMS-RESTRICT"><span class="term"><code class="literal">RESTRICT</code></span> <a href="#SQL-ALTERTABLE-PARMS-RESTRICT" class="id_link">#</a></dt><dd><p>744        Refuse to drop the column or constraint if there are any dependent745        objects. This is the default behavior.746       </p></dd><dt id="SQL-ALTERTABLE-PARMS-TRIGGER-NAME"><span class="term"><em class="replaceable"><code>trigger_name</code></em></span> <a href="#SQL-ALTERTABLE-PARMS-TRIGGER-NAME" class="id_link">#</a></dt><dd><p>747        Name of a single trigger to disable or enable.748       </p></dd><dt id="SQL-ALTERTABLE-PARMS-ALL"><span class="term"><code class="literal">ALL</code></span> <a href="#SQL-ALTERTABLE-PARMS-ALL" class="id_link">#</a></dt><dd><p>749        Disable or enable all triggers belonging to the table.750        (This requires superuser privilege if any of the triggers are751        internally generated constraint triggers, such as those that are used752        to implement foreign key constraints or deferrable uniqueness and753        exclusion constraints.)754       </p></dd><dt id="SQL-ALTERTABLE-PARMS-USER"><span class="term"><code class="literal">USER</code></span> <a href="#SQL-ALTERTABLE-PARMS-USER" class="id_link">#</a></dt><dd><p>755        Disable or enable all triggers belonging to the table except for756        internally generated constraint triggers, such as those that are used757        to implement foreign key constraints or deferrable uniqueness and758        exclusion constraints.759       </p></dd><dt id="SQL-ALTERTABLE-PARMS-INDEX-NAME"><span class="term"><em class="replaceable"><code>index_name</code></em></span> <a href="#SQL-ALTERTABLE-PARMS-INDEX-NAME" class="id_link">#</a></dt><dd><p>760        The name of an existing index.761       </p></dd><dt id="SQL-ALTERTABLE-PARMS-STORAGE-PARAMETER"><span class="term"><em class="replaceable"><code>storage_parameter</code></em></span> <a href="#SQL-ALTERTABLE-PARMS-STORAGE-PARAMETER" class="id_link">#</a></dt><dd><p>762        The name of a table storage parameter.763       </p></dd><dt id="SQL-ALTERTABLE-PARMS-VALUE"><span class="term"><em class="replaceable"><code>value</code></em></span> <a href="#SQL-ALTERTABLE-PARMS-VALUE" class="id_link">#</a></dt><dd><p>764        The new value for a table storage parameter.765        This might be a number or a word depending on the parameter.766       </p></dd><dt id="SQL-ALTERTABLE-PARMS-PARENT-TABLE"><span class="term"><em class="replaceable"><code>parent_table</code></em></span> <a href="#SQL-ALTERTABLE-PARMS-PARENT-TABLE" class="id_link">#</a></dt><dd><p>767        A parent table to associate or de-associate with this table.768       </p></dd><dt id="SQL-ALTERTABLE-PARMS-NEW-OWNER"><span class="term"><em class="replaceable"><code>new_owner</code></em></span> <a href="#SQL-ALTERTABLE-PARMS-NEW-OWNER" class="id_link">#</a></dt><dd><p>769        The user name of the new owner of the table.770       </p></dd><dt id="SQL-ALTERTABLE-PARMS-NEW-ACCESS-METHOD"><span class="term"><em class="replaceable"><code>new_access_method</code></em></span> <a href="#SQL-ALTERTABLE-PARMS-NEW-ACCESS-METHOD" class="id_link">#</a></dt><dd><p>771        The name of the access method to which the table will be converted.772       </p></dd><dt id="SQL-ALTERTABLE-PARMS-NEW-TABLESPACE"><span class="term"><em class="replaceable"><code>new_tablespace</code></em></span> <a href="#SQL-ALTERTABLE-PARMS-NEW-TABLESPACE" class="id_link">#</a></dt><dd><p>773        The name of the tablespace to which the table will be moved.774       </p></dd><dt id="SQL-ALTERTABLE-PARMS-NEW-SCHEMA"><span class="term"><em class="replaceable"><code>new_schema</code></em></span> <a href="#SQL-ALTERTABLE-PARMS-NEW-SCHEMA" class="id_link">#</a></dt><dd><p>775        The name of the schema to which the table will be moved.776       </p></dd><dt id="SQL-ALTERTABLE-PARMS-PARTITION-NAME"><span class="term"><em class="replaceable"><code>partition_name</code></em></span> <a href="#SQL-ALTERTABLE-PARMS-PARTITION-NAME" class="id_link">#</a></dt><dd><p>777        The name of the table to attach as a new partition or to detach from this table.778       </p></dd><dt id="SQL-ALTERTABLE-PARMS-PARTITION-BOUND-SPEC"><span class="term"><em class="replaceable"><code>partition_bound_spec</code></em></span> <a href="#SQL-ALTERTABLE-PARMS-PARTITION-BOUND-SPEC" class="id_link">#</a></dt><dd><p>779        The partition bound specification for a new partition.  Refer to780        <a class="xref" href="sql-createtable.html" title="CREATE TABLE"><span class="refentrytitle">CREATE TABLE</span></a> for more details on the syntax of the same.781       </p></dd></dl></div></div><div class="refsect1" id="SQL-ALTERTABLE-NOTES"><h2>Notes</h2><p>782    The key word <code class="literal">COLUMN</code> is noise and can be omitted.783   </p><p>784    When a column is added with <code class="literal">ADD COLUMN</code> and a785    non-volatile <code class="literal">DEFAULT</code> is specified, the default is786    evaluated at the time of the statement and the result stored in the787    table's metadata.  That value will be used for the column for all existing788    rows.  If no <code class="literal">DEFAULT</code> is specified, NULL is used.  In789    neither case is a rewrite of the table required.790   </p><p>791    Adding a column with a volatile <code class="literal">DEFAULT</code> or792    changing the type of an existing column will require the entire table and793    its indexes to be rewritten. As an exception, when changing the type of an794    existing column, if the <code class="literal">USING</code> clause does not change795    the column contents and the old type is either binary coercible to the new796    type or an unconstrained domain over the new type, a table rewrite is not797    needed. However, indexes must always be rebuilt unless the system can798    verify that the new index would be logically equivalent to the existing799    one.  For example, if the collation for a column has been changed, an index800    rebuild is always required because the new sort order might be different.801    However, in the absence of a collation change, a column can be changed802    from <code class="type">text</code> to <code class="type">varchar</code> (or vice versa) without803    rebuilding the indexes because these data types sort identically.804    Table and/or index rebuilds may take a805    significant amount of time for a large table; and will temporarily require806    as much as double the disk space.807   </p><p>808    Adding a <code class="literal">CHECK</code> or <code class="literal">NOT NULL</code> constraint requires809    scanning the table to verify that existing rows meet the constraint,810    but does not require a table rewrite.811   </p><p>812    Similarly, when attaching a new partition it may be scanned to verify that813    existing rows meet the partition constraint.814   </p><p>815    The main reason for providing the option to specify multiple changes816    in a single <code class="command">ALTER TABLE</code> is that multiple table scans or817    rewrites can thereby be combined into a single pass over the table.818   </p><p>819    Scanning a large table to verify a new foreign key or check constraint820    can take a long time, and other updates to the table are locked out821    until the <code class="command">ALTER TABLE ADD CONSTRAINT</code> command is822    committed.  The main purpose of the <code class="literal">NOT VALID</code>823    constraint option is to reduce the impact of adding a constraint on824    concurrent updates.  With <code class="literal">NOT VALID</code>,825    the <code class="command">ADD CONSTRAINT</code> command does not scan the table826    and can be committed immediately.  After that, a <code class="literal">VALIDATE827    CONSTRAINT</code> command can be issued to verify that existing rows828    satisfy the constraint.  The validation step does not need to lock out829    concurrent updates, since it knows that other transactions will be830    enforcing the constraint for rows that they insert or update; only831    pre-existing rows need to be checked.  Hence, validation acquires only832    a <code class="literal">SHARE UPDATE EXCLUSIVE</code> lock on the table being833    altered.  (If the constraint is a foreign key then a <code class="literal">ROW834    SHARE</code> lock is also required on the table referenced by the835    constraint.)  In addition to improving concurrency, it can be useful to836    use <code class="literal">NOT VALID</code> and <code class="literal">VALIDATE837    CONSTRAINT</code> in cases where the table is known to contain838    pre-existing violations.  Once the constraint is in place, no new839    violations can be inserted, and the existing problems can be corrected840    at leisure until <code class="literal">VALIDATE CONSTRAINT</code> finally841    succeeds.842   </p><p>843    The <code class="literal">DROP COLUMN</code> form does not physically remove844    the column, but simply makes it invisible to SQL operations.  Subsequent845    insert and update operations in the table will store a null value for the846    column. Thus, dropping a column is quick but it will not immediately847    reduce the on-disk size of your table, as the space occupied848    by the dropped column is not reclaimed.  The space will be849    reclaimed over time as existing rows are updated.850   </p><p>851    To force immediate reclamation of space occupied by a dropped column,852    you can execute one of the forms of <code class="command">ALTER TABLE</code> that853    performs a rewrite of the whole table.  This results in reconstructing854    each row with the dropped column replaced by a null value.855   </p><p>856    The rewriting forms of <code class="command">ALTER TABLE</code> are not MVCC-safe.857    After a table rewrite, the table will appear empty to concurrent858    transactions, if they are using a snapshot taken before the rewrite859    occurred.  See <a class="xref" href="mvcc-caveats.html" title="13.6. Caveats">Section 13.6</a> for more details.860   </p><p>861    The <code class="literal">USING</code> option of <code class="literal">SET DATA TYPE</code> can actually862    specify any expression involving the old values of the row; that is, it863    can refer to other columns as well as the one being converted.  This allows864    very general conversions to be done with the <code class="literal">SET DATA TYPE</code>865    syntax.  Because of this flexibility, the <code class="literal">USING</code>866    expression is not applied to the column's default value (if any); the867    result might not be a constant expression as required for a default.868    This means that when there is no implicit or assignment cast from old to869    new type, <code class="literal">SET DATA TYPE</code> might fail to convert the default even870    though a <code class="literal">USING</code> clause is supplied.  In such cases,871    drop the default with <code class="literal">DROP DEFAULT</code>, perform the <code class="literal">ALTER872    TYPE</code>, and then use <code class="literal">SET DEFAULT</code> to add a suitable new873    default.  Similar considerations apply to indexes and constraints involving874    the column.875   </p><p>876    If a table has any descendant tables, it is not permitted to add,877    rename, or change the type of a column in the parent table without doing878    the same to the descendants.  This ensures that the descendants always879    have columns matching the parent.  Similarly, a <code class="literal">CHECK</code>880    constraint cannot be renamed in the parent without also renaming it in881    all descendants, so that <code class="literal">CHECK</code> constraints also match882    between the parent and its descendants.  (That restriction does not apply883    to index-based constraints, however.)884    Also, because selecting from the parent also selects from its descendants,885    a constraint on the parent cannot be marked valid unless it is also marked886    valid for those descendants.  In all of these cases, <code class="command">ALTER TABLE887    ONLY</code> will be rejected.888   </p><p>889    A recursive <code class="literal">DROP COLUMN</code> operation will remove a890    descendant table's column only if the descendant does not inherit891    that column from any other parents and never had an independent892    definition of the column.  A nonrecursive <code class="literal">DROP893    COLUMN</code> (i.e., <code class="command">ALTER TABLE ONLY ... DROP894    COLUMN</code>) never removes any descendant columns, but895    instead marks them as independently defined rather than inherited.896    A nonrecursive <code class="literal">DROP COLUMN</code> command will fail for a897    partitioned table, because all partitions of a table must have the same898    columns as the partitioning root.899   </p><p>900    The actions for identity columns (<code class="literal">ADD901    GENERATED</code>, <code class="literal">SET</code> etc., <code class="literal">DROP902    IDENTITY</code>), as well as the actions903    <code class="literal">CLUSTER</code>, <code class="literal">OWNER</code>,904    and <code class="literal">TABLESPACE</code> never recurse to descendant tables;905    that is, they always act as though <code class="literal">ONLY</code> were specified.906    Actions affecting trigger states recurse to partitions of partitioned907    tables (unless <code class="literal">ONLY</code> is specified), but never to908    traditional-inheritance descendants.909    Adding a constraint recurses only for <code class="literal">CHECK</code> constraints910    that are not marked <code class="literal">NO INHERIT</code>.911   </p><p>912    Changing any part of a system catalog table is not permitted.913   </p><p>914    Refer to <a class="xref" href="sql-createtable.html" title="CREATE TABLE"><span class="refentrytitle">CREATE TABLE</span></a> for a further description of valid915    parameters. <a class="xref" href="ddl.html" title="Chapter 5. Data Definition">Chapter 5</a> has further information on916    inheritance.917   </p></div><div class="refsect1" id="id-1.9.3.35.8"><h2>Examples</h2><p>918   To add a column of type <code class="type">varchar</code> to a table:919</p><pre class="programlisting">920ALTER TABLE distributors ADD COLUMN address varchar(30);921</pre><p>922   That will cause all existing rows in the table to be filled with null923   values for the new column.924  </p><p>925   To add a column with a non-null default:926</p><pre class="programlisting">927ALTER TABLE measurements928  ADD COLUMN mtime timestamp with time zone DEFAULT now();929</pre><p>930   Existing rows will be filled with the current time as the value of the931   new column, and then new rows will receive the time of their insertion.932  </p><p>933   To add a column and fill it with a value different from the default to934   be used later:935</p><pre class="programlisting">936ALTER TABLE transactions937  ADD COLUMN status varchar(30) DEFAULT 'old',938  ALTER COLUMN status SET default 'current';939</pre><p>940   Existing rows will be filled with <code class="literal">old</code>, but then941   the default for subsequent commands will be <code class="literal">current</code>.942   The effects are the same as if the two sub-commands had been issued943   in separate <code class="command">ALTER TABLE</code> commands.944  </p><p>945   To drop a column from a table:946</p><pre class="programlisting">947ALTER TABLE distributors DROP COLUMN address RESTRICT;948</pre><p>949  </p><p>950   To change the types of two existing columns in one operation:951</p><pre class="programlisting">952ALTER TABLE distributors953    ALTER COLUMN address TYPE varchar(80),954    ALTER COLUMN name TYPE varchar(100);955</pre><p>956  </p><p>957   To change an integer column containing Unix timestamps to <code class="type">timestamp958   with time zone</code> via a <code class="literal">USING</code> clause:959</p><pre class="programlisting">960ALTER TABLE foo961    ALTER COLUMN foo_timestamp SET DATA TYPE timestamp with time zone962    USING963        timestamp with time zone 'epoch' + foo_timestamp * interval '1 second';964</pre><p>965  </p><p>966   The same, when the column has a default expression that won't automatically967   cast to the new data type:968</p><pre class="programlisting">969ALTER TABLE foo970    ALTER COLUMN foo_timestamp DROP DEFAULT,971    ALTER COLUMN foo_timestamp TYPE timestamp with time zone972    USING973        timestamp with time zone 'epoch' + foo_timestamp * interval '1 second',974    ALTER COLUMN foo_timestamp SET DEFAULT now();975</pre><p>976  </p><p>977   To rename an existing column:978</p><pre class="programlisting">979ALTER TABLE distributors RENAME COLUMN address TO city;980</pre><p>981  </p><p>982   To rename an existing table:983</p><pre class="programlisting">984ALTER TABLE distributors RENAME TO suppliers;985</pre><p>986  </p><p>987   To rename an existing constraint:988</p><pre class="programlisting">989ALTER TABLE distributors RENAME CONSTRAINT zipchk TO zip_check;990</pre><p>991  </p><p>992   To add a not-null constraint to a column:993</p><pre class="programlisting">994ALTER TABLE distributors ALTER COLUMN street SET NOT NULL;995</pre><p>996   To remove a not-null constraint from a column:997</p><pre class="programlisting">998ALTER TABLE distributors ALTER COLUMN street DROP NOT NULL;999</pre><p>1000  </p><p>1001   To add a check constraint to a table and all its children:1002</p><pre class="programlisting">1003ALTER TABLE distributors ADD CONSTRAINT zipchk CHECK (char_length(zipcode) = 5);1004</pre><p>1005  </p><p>1006   To add a check constraint only to a table and not to its children:1007</p><pre class="programlisting">1008ALTER TABLE distributors ADD CONSTRAINT zipchk CHECK (char_length(zipcode) = 5) NO INHERIT;1009</pre><p>1010   (The check constraint will not be inherited by future children, either.)1011  </p><p>1012   To remove a check constraint from a table and all its children:1013</p><pre class="programlisting">1014ALTER TABLE distributors DROP CONSTRAINT zipchk;1015</pre><p>1016  </p><p>1017   To remove a check constraint from one table only:1018</p><pre class="programlisting">1019ALTER TABLE ONLY distributors DROP CONSTRAINT zipchk;1020</pre><p>1021   (The check constraint remains in place for any child tables.)1022  </p><p>1023   To add a foreign key constraint to a table:1024</p><pre class="programlisting">1025ALTER TABLE distributors ADD CONSTRAINT distfk FOREIGN KEY (address) REFERENCES addresses (address);1026</pre><p>1027  </p><p>1028   To add a foreign key constraint to a table with the least impact on other work:1029</p><pre class="programlisting">1030ALTER TABLE distributors ADD CONSTRAINT distfk FOREIGN KEY (address) REFERENCES addresses (address) NOT VALID;1031ALTER TABLE distributors VALIDATE CONSTRAINT distfk;1032</pre><p>1033  </p><p>1034   To add a (multicolumn) unique constraint to a table:1035</p><pre class="programlisting">1036ALTER TABLE distributors ADD CONSTRAINT dist_id_zipcode_key UNIQUE (dist_id, zipcode);1037</pre><p>1038  </p><p>1039   To add an automatically named primary key constraint to a table, noting1040   that a table can only ever have one primary key:1041</p><pre class="programlisting">1042ALTER TABLE distributors ADD PRIMARY KEY (dist_id);1043</pre><p>1044  </p><p>1045   To move a table to a different tablespace:1046</p><pre class="programlisting">1047ALTER TABLE distributors SET TABLESPACE fasttablespace;1048</pre><p>1049  </p><p>1050   To move a table to a different schema:1051</p><pre class="programlisting">1052ALTER TABLE myschema.distributors SET SCHEMA yourschema;1053</pre><p>1054  </p><p>1055   To recreate a primary key constraint, without blocking updates while the1056   index is rebuilt:1057</p><pre class="programlisting">1058CREATE UNIQUE INDEX CONCURRENTLY dist_id_temp_idx ON distributors (dist_id);1059ALTER TABLE distributors DROP CONSTRAINT distributors_pkey,1060    ADD CONSTRAINT distributors_pkey PRIMARY KEY USING INDEX dist_id_temp_idx;1061</pre><p>1062   To attach a partition to a range-partitioned table:1063</p><pre class="programlisting">1064ALTER TABLE measurement1065    ATTACH PARTITION measurement_y2016m07 FOR VALUES FROM ('2016-07-01') TO ('2016-08-01');1066</pre><p>1067   To attach a partition to a list-partitioned table:1068</p><pre class="programlisting">1069ALTER TABLE cities1070    ATTACH PARTITION cities_ab FOR VALUES IN ('a', 'b');1071</pre><p>1072   To attach a partition to a hash-partitioned table:1073</p><pre class="programlisting">1074ALTER TABLE orders1075    ATTACH PARTITION orders_p4 FOR VALUES WITH (MODULUS 4, REMAINDER 3);1076</pre><p>1077   To attach a default partition to a partitioned table:1078</p><pre class="programlisting">1079ALTER TABLE cities1080    ATTACH PARTITION cities_partdef DEFAULT;1081</pre><p>1082   To detach a partition from a partitioned table:1083</p><pre class="programlisting">1084ALTER TABLE measurement1085    DETACH PARTITION measurement_y2015m12;1086</pre></div><div class="refsect1" id="id-1.9.3.35.9"><h2>Compatibility</h2><p>1087   The forms <code class="literal">ADD</code> (without <code class="literal">USING INDEX</code>),1088   <code class="literal">DROP [COLUMN]</code>, <code class="literal">DROP IDENTITY</code>, <code class="literal">RESTART</code>,1089   <code class="literal">SET DEFAULT</code>, <code class="literal">SET DATA TYPE</code> (without <code class="literal">USING</code>),1090   <code class="literal">SET GENERATED</code>, and <code class="literal">SET <em class="replaceable"><code>sequence_option</code></em></code>1091   conform with the SQL standard.  The other forms are1092   <span class="productname">PostgreSQL</span> extensions of the SQL standard.1093   Also, the ability to specify more than one manipulation in a single1094   <code class="command">ALTER TABLE</code> command is an extension.1095  </p><p>1096   <code class="command">ALTER TABLE DROP COLUMN</code> can be used to drop the only1097   column of a table, leaving a zero-column table.  This is an1098   extension of SQL, which disallows zero-column tables.1099  </p></div><div class="refsect1" id="id-1.9.3.35.10"><h2>See Also</h2><span class="simplelist"><a class="xref" href="sql-createtable.html" title="CREATE TABLE"><span class="refentrytitle">CREATE TABLE</span></a></span></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="sql-altersystem.html" title="ALTER SYSTEM">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sql-commands.html" title="SQL Commands">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="sql-altertablespace.html" title="ALTER TABLESPACE">Next</a></td></tr><tr><td width="40%" align="left" valign="top">ALTER SYSTEM </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> ALTER TABLESPACE</td></tr></table></div></body></html>
codekingpro/portable-devtools · Team Ai